The primary function of industrial fans is to provide a large fluid flow, with general utility in/for processes such as combustion, ventilation, aeration, particulate transport, exhaust, cooling, air-cleaning and drying. Fluid flow delivery is accomplished by rotating a number of blades, connected to a hub and shaft, and driven by a motor or turbine. Industrial fans are generally categorized as being either centrifugal or axial in nature, with each having a characteristic fluid flow path indicative of their monikers.
Centrifugal fans use a rotating impeller to increase the velocity of a fluid. As the fluid moves from the impeller hub to the fan blade tips, it gains kinetic energy, which in turn is converted to a static pressure increase as the air slows in advance of discharge.
Axial fans move fluid along the axis of the fan. The fluid is pressurized by the aerodynamic lift, i.e., axial forces, generated by the fan blades. Propeller, tubeaxial and vane axial fans are well know variants of this style fan, with the tubeaxial and vane axial being more complex versions of the propeller fan.
Of the two, centrifugal fans are most commonly used in industry owing to their ability to generate high pressures with high efficiency. Moreover, centrifugal fans can be constructed to accommodate harsh operating conditions.
For example, composite assemblies are generally known and applied in and for a variety of contexts, e.g., and without limitation, where inertness, increased strength, and/or reduced weight are required or perceived as desirable/advantageous. In the instant setting, industrial fans, for example, may be, and oftentimes must be, among other things, sufficiently inert to hold up to process rigors and air streams characterized by deleterious components.
Fiber/fabric reinforced plastic/polymer (FRP) construction is commonly utilized for such settings/applications, with fiberglass or carbon fiber construction being prevalent. As is generally known and understood, FRP is a composite material made of a polymer matrix reinforced with fibers. In addition to glass and carbon fibers, aramid (e.g. Kevlar®) fibers as well as cellulosic fibers are known. Moreover, inorganic particulates are known as a “fiber” substitute. As to the matrix, the polymer is usually an epoxy, vinyl ester, or polyester thermosetting plastic.
One known and not infrequently encountered industrial air handling scenario implicates a backward curved high pressure composite fan. Such fan includes a backward curved fan blade in the context of an industrial fan designed for handling particulate-free, corrosive or caustic air in high pressure applications where conventional steel and stainless steel fans would corrode. All of the parts that are exposed to the airstream are constructed of high-quality corrosion resistant materials to avoid material breakdown from most chemicals.
Typical or representative industries that utilize this style of fan include fertilizer, metal and mineral processing, pulp-and-paper, steel processing, petrochemical and pharmaceutical plants, and water and wastewater-treatment facilities. Typical or representative applications include, fume control/exhaust, odor control, oil mist emissions, pollution/emissions control, process control/heating/cooling, and scrubbers.
Generally, but not necessarily characteristic of such representative applications is a requirement for a relatively high fluid flow at a medium to high discharge pressure. In an effort to acheive greater capacity and efficiency, composite single thickness fan blades (i.e., monolithic composite laminates) have been adapted for, among other things, weight reduction, with fan blades known to comprise “sandwich” composite structures, i.e., two high strength skins or facings separated by a core material/element, e.g., a foam core element comprised of cellular polyvinyl chloride or the like. With improved strength-to-weight ratios, such fan blades offer better performance and operating economy.
While fan blades per se have been so adapted, realization of hoped for performance advantage and improved operating economy have yet to be realized/fully realized owing to shortcomings of fan wheels/fan assemblies so characterized. Such fan blades traverse a backplate and a wheel cone (a/k/a inlet cone or inlet plate) with affixation of each blade to each of the backplate and wheel cone via primary and secondary bonding in the form of adhesive and FRP joints respectively. Higher capacity has generally been hampered by the interface for and between the fan blade and the backplate and wheel cone, namely a less than optimal integration of the fan blades to/with the backplate and wheel cone.
In light of the forgoing, it is generally believed advantageous to improve select components of industrial fans in furtherance of at least satisfying performance and maintenance objectives. Moreover, it is likewise believed advantageous to improve one or more relationships for, between, and/or among such select components of such fan, or fans more generally. More particularly, it is believed desirable and advantageous to provide an improved interface and/or operative integration for, between and among a composite fan blade and its associated fan wheel elements, namely, a backplate and a wheel cone thereof.